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      <title>数据库设计与优化 - 交互式测验</title>
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          color: white;
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          border-radius: 8px;
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            border-radius: 12px;
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      </style>
    </head>
    <body>
      <div class="main-wrapper">
          <div class="quiz-container">
            <div class="quiz-header">
              <h1>数据库设计与优化 - 交互式测验</h1>
              <p>检验你对文档内容的理解程度</p>
            </div>
            <div id="quiz-content">
                <div class="quiz-body">
                    <div class="progress-bar">
                        <div id="progress-indicator"></div>
                    </div>
                    <div id="question-container">
                      <p id="question-text"></p>
                      <ul class="options-list" id="options-list"></ul>
                    </div>
                    <div id="result-container"></div>
                    <div id="hint-container" class="hint-container"></div>
                </div>
                <div class="quiz-footer" id="quiz-footer">
                  <button id="prev-btn" class="nav-btn">上一题</button>
                  <button id="hint-btn" class="nav-btn" style="background-color: #ffc107; color: #333; box-shadow: 0 4px 12px rgba(255,193,7,0.3);">提示</button>
                  <button id="next-btn" class="nav-btn">下一题</button>
                </div>
            </div>
          </div>
      </div>

      <script>
        const quizData = [
  {
    "question": "根据文档，在设计“主从复制”架构时，其主要目的是为了解决什么问题？",
    "options": [
      "通过读写分离来提高系统的并发处理能力和可用性。",
      "主要用于数据备份，确保主数据库故障后能快速恢复。",
      "解决单台服务器存储容量不足的问题。",
      "保证跨多个数据库的事务强一致性。"
    ],
    "correctAnswerIndex": 0,
    "explanation": "主从复制架构的核心优势在于实现了读写分离。主库负责处理写操作（INSERT, UPDATE, DELETE），而一个或多个从库可以处理读操作（SELECT）。这样可以将读请求的负载从主库上分担出去，从而显著减轻主库的压力，提高整个系统的并发查询能力和容错性。",
    "source": "文档中「2.2 主从复制与读写分离」部分",
    "hint": "文档提到，该方案能够“减轻主库的负担，提高系统的并发能力”。"
  },
  {
    "question": "文档中提到了多种索引类型，如果一个数据列的基数非常低（例如，存储性别的列，只有'男'、'女'、'未知'等几个固定值），哪种索引类型最适用？",
    "options": [
      "哈希索引 (Hash Index)",
      "B-Tree 索引 (B-tree Index)",
      "全文索引 (Full-text Index)",
      "位图索引 (Bitmap Index)"
    ],
    "correctAnswerIndex": 3,
    "explanation": "位图索引特别适用于基数较低的列。基数是指列中不同值的数量。对于像性别、状态这类只有少数几个可能值的列，位图索引可以通过使用位图（bitmap）来高效地表示每行数据是否具有某个特定值，从而在执行查询时（尤其是涉及多个低基数列的AND/OR查询）提供非常高的性能。",
    "source": "文档中「3.1 常见索引类型」部分",
    "hint": "在索引类型介绍中，哪一种被明确描述为“适用于低基数的列（例如性别、状态等）”？"
  },
  {
    "question": "在事务的ACID四个特性中，哪一个特性保证了事务中的所有操作要么全部成功执行，要么在任意环节失败后全部回滚到事务开始前的状态？",
    "options": [
      "持久性 (Durability)",
      "一致性 (Consistency)",
      "原子性 (Atomicity)",
      "隔离性 (Isolation)"
    ],
    "correctAnswerIndex": 2,
    "explanation": "原子性（Atomicity）是事务最基本的特性，它要求事务是一个不可分割的工作单元。事务内的所有操作，必须作为一个整体被提交或回滚。如果任何一个操作失败，整个事务都会被撤销，数据库将恢复到事务开始之前的状态，就像这个事务从未发生过一样。",
    "source": "文档中「5.1 事务的ACID特性」部分",
    "hint": "这个特性确保了事务的“全有或全无”（all-or-nothing）原则。"
  },
  {
    "question": "文档强调在查询优化中应“避免SELECT *查询”。这样做的主要原因是什么？",
    "options": [
      "因为它会阻止数据库查询优化器使用索引。",
      "为了减少不必要的数据在数据库服务器和客户端之间的传输。",
      "因为它会导致事务隔离级别自动降级，引发数据不一致。",
      "SELECT * 是非标准SQL语法，可能在某些数据库中执行失败。"
    ],
    "correctAnswerIndex": 1,
    "explanation": "使用`SELECT *`会查询出表中的所有列，即使你的应用程序只需要其中的几列。这会增加网络I/O的负担，浪费网络带宽，并可能增加应用程序处理数据的内存消耗。明确指定你需要的列（例如 `SELECT id, name, email`）是一种高效的编程习惯，可以显著减少不必要的数据传输，从而提升性能。",
    "source": "文档中「4.1 查询语句优化」部分",
    "hint": "思考一下从数据库获取数据到应用程序展示的整个流程，哪个环节的开销会因为查询了不需要的字段而增加？"
  },
  {
    "question": "关于数据库规范化与去规范化，以下哪个描述是正确的？",
    "options": [
      "规范化的主要目标是通过增加数据冗余来提升查询速度。",
      "去规范化是为了消除数据更新异常，保证数据的完整性。",
      "在高性能要求的场景下，可能会采用去规范化来减少复杂的JOIN查询。",
      "规范化和去规范化都旨在最大限度地节省数据库存储空间。"
    ],
    "correctAnswerIndex": 2,
    "explanation": "数据库规范化旨在减少数据冗余和依赖，从而提高数据完整性。然而，高度规范化的数据模型常常需要通过多个表的连接（JOIN）才能获取完整信息，这在查询频繁的系统中可能成为性能瓶颈。因此，为了优化查询性能，有时会故意引入少量冗余数据（去规范化），通过空间换时间的方式来避免或减少昂贵的JOIN操作。",
    "source": "文档中「1.2 规范化与去规范化」部分",
    "hint": "文档提到规范化“可能影响查询性能”，因此在某些场景下会考虑一种相反的策略。"
  },
  {
    "question": "在数据库事务隔离级别中，哪个级别可能导致“脏读”（即一个事务读取到另一个事务尚未提交的数据）？",
    "options": [
      "可重复读 (Repeatable Read)",
      "串行化 (Serializable)",
      "读未提交 (Read Uncommitted)",
      "读已提交 (Read Committed)"
    ],
    "correctAnswerIndex": 2,
    "explanation": "“读未提交”是最低的事务隔离级别。在此级别下，一个事务可以看到其他事务尚未提交的修改。如果那个修改数据的事务最终回滚了，那么第一个事务读取到的就是无效的、“脏”的数据，这可能导致严重的数据一致性问题。",
    "source": "文档中「5.2 事务隔离级别」部分",
    "hint": "顾名思义，哪个隔离级别的名称就暗示了它可以读取“还未提交”的数据？"
  },
  {
    "question": "文档指出，拥有过多的索引可能会对数据库性能产生负面影响。这种负面影响主要体现在哪个方面？",
    "options": [
      "显著降低所有`SELECT`查询的速度。",
      "导致数据库备份和恢复操作失败。",
      "增加数据插入（INSERT）、更新（UPDATE）和删除（DELETE）操作的开销。",
      "使数据库无法创建外键约束。"
    ],
    "correctAnswerIndex": 2,
    "explanation": "虽然索引能极大地加速数据查询（SELECT），但它并非没有成本。每当对表中的数据进行插入、更新或删除操作时，数据库不仅需要修改数据本身，还必须同步更新该表上的所有相关索引。索引越多，每次数据修改时需要维护的索引结构就越多，从而导致写操作的性能下降。",
    "source": "文档中「3.2 索引的选择与管理」部分",
    "hint": "文档中提到，“过多的索引会导致插入、更新和删除操作的性能下降”。"
  }
];
        console.log("Quiz Data:", JSON.parse(JSON.stringify(quizData))); // 添加这行用于调试，以可展开的JSON格式输出
        
        let currentQuestionIndex = 0;
        let score = 0;
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        const quizContentEl = document.getElementById('quiz-content');
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        const prevBtn = document.getElementById('prev-btn');
        const nextBtn = document.getElementById('next-btn');
        const hintBtn = document.getElementById('hint-btn');
        const hintContainerEl = document.getElementById('hint-container');

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          optionsListEl.innerHTML = '';
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            return;
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            nextBtn.style.display = 'block';
            hintBtn.style.display = 'block'; // 显示提示按钮

            prevBtn.disabled = currentQuestionIndex === 0;
            nextBtn.disabled = false; // 最后一题时，下一题按钮不禁用，而是用于显示报告
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            // 如果当前问题没有提示，则禁用提示按钮并隐藏提示内容
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                hintBtn.disabled = true;
                hintContainerEl.style.display = 'none';
                hintContainerEl.textContent = ''; // 清除旧的提示内容
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                hintBtn.disabled = false;
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        function showResult(isCorrect, questionData) {
            resultContainerEl.innerHTML = ''; // 清空之前的结果
            const resultBox = document.createElement('div');
            resultBox.className = `result-box ${isCorrect ? 'correct' : 'incorrect'}`;
            
            let html = `<h3>${isCorrect ? '回答正确！' : '回答错误'}</h3>`;
            if (!isCorrect) {
                html += `<p><strong>正确答案是：</strong> ${questionData.options[questionData.correctAnswerIndex]}</p>`;
            }
            html += `<div class="explanation-text">${questionData.explanation}</div>`;
            html += `<div class="source-text">来源: ${questionData.source}</div>`;
            
            resultBox.innerHTML = html;
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                // 高亮正确答案
                if (index === questionData.correctAnswerIndex) {
                    child.classList.add('correct'); // 需要添加CSS样式
                    child.style.backgroundColor = '#d4edda';
                    child.style.borderColor = '#c3e6cb';
                }
                // 如果选错了，高亮错误选项
                if (!isCorrect && index === userAnswers[currentQuestionIndex]) {
                    child.classList.add('incorrect'); // 需要添加CSS样式
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                    child.style.borderColor = '#f5c6cb';
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                hintContainerEl.style.display = 'none';
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        function showFinalScore() {
            document.querySelector('.quiz-body').style.display = 'none';
            document.getElementById('quiz-footer').style.display = 'none';

            const correctCount = score;
            const totalQuestions = quizData.length;
            const answeredCount = userAnswers.filter(a => a !== null).length;
            const wrongCount = answeredCount - correctCount;
            const skippedCount = totalQuestions - answeredCount;
            const accuracy = totalQuestions > 0 ? Math.round((correctCount / totalQuestions) * 100) : 0;
            const errorRate = totalQuestions > 0 ? Math.round((wrongCount / totalQuestions) * 100) : 0;

            const finalScoreHtml =
                '<div class="final-score-container">' +
                '<h2>答题报告</h2>' +
                '<div class="score-summary">' +
                '<div class="score-card">' +
                '<h3>得分</h3>' +
                '<p>' + correctCount + ' / ' + totalQuestions + '</p>' +
                '</div>' +
                '<div class="score-card">' +
                '<h3>正确率</h3>' +
                '<p>' + accuracy + '%</p>' +
                '</div>' +
                '<div class="score-card">' +
                '<h3>错误率</h3>' +
                '<p>' + errorRate + '%</p>' +
                '</div>' +
                '<div class="score-card score-details">' +
                '<table>' +
                '<tr><td>正确</td><td>' + correctCount + '</td></tr>' +
                '<tr><td>错误</td><td>' + wrongCount + '</td></tr>' +
                '<tr><td>未答</td><td>' + skippedCount + '</td></tr>' +
                '</table>' +
                '</div>' +
                '</div>' +
                '<div class="report-actions">' +
                '<button id="review-btn">回顾测验</button>' +
                '<button class="primary" onclick="location.reload()">再试一次</button>' +
                '</div>' +
                '</div>';

            let reportEl = document.querySelector('.final-score-container');
            if (reportEl) {
                reportEl.remove();
            }
            quizContentEl.insertAdjacentHTML('beforeend', finalScoreHtml);
            document.getElementById('review-btn').addEventListener('click', reviewQuiz);
        }

        function reviewQuiz() {
            const reportEl = document.querySelector('.final-score-container');
            if (reportEl) {
                reportEl.remove();
            }

            document.querySelector('.quiz-body').style.display = 'block';
            document.getElementById('quiz-footer').style.display = 'flex';
            
            currentQuestionIndex = 0;
            loadQuestion();
            updateNavigationButtons(); // Ensure nav buttons are correctly displayed
        }

        // Event Delegation for options
        optionsListEl.addEventListener('click', (event) => {
            if (event.target && event.target.matches('li.option-item')) {
                // Check if the question has already been answered
                if (userAnswers[currentQuestionIndex] === null) {
                    const selectedIndex = parseInt(event.target.dataset.index, 10);
                    selectOption(selectedIndex);
                }
            }
        });

        prevBtn.addEventListener('click', goToPreviousQuestion);
        nextBtn.addEventListener('click', goToNextQuestion);
        hintBtn.addEventListener('click', showHint);
        
        // 初始加载
        loadQuestion();
      </script>
    </body>
    </html>
  